Morphological Classification of Mandibular Central Incisor Root Canals and Incidence of Accessory Root Canals in Japanese People Using Micro-Computed Tomography

This study examined the root canal morphology and the incidence of accessory root canals in mandibular central incisors, factors believed to influence the success of root canal treatment. Micro-computed tomography scans were conducted on Japanese mandibular central incisors from the Department of Anatomy collection at Tokyo Dental College. Morphological types were classified according to Vertucci’s system, and the presence of accessory root canals was analyzed based on three-dimensional reconstructions. All examined incisors were found to have single roots. When classified by the number of main root canals, 87% were Type I with a single complete root canal, and 10% were Type III, with a single root canal splitting into two and then fusing again, figures generally consistent with those of previous reports. Types IV and VII, with a lingual root canal, were also present, though at low frequencies. The incidence of accessory root canals was 36.0%, a higher rate than previously reported. An investigation of the shape of the root canal in cross-section showed that, in the horizontal plane perpendicular to the tooth axis at a distance of 9 mm from the apex (A plane), the circular shape was the most common, whereas in the horizontal plane perpendicular to the tooth axis at a distance of 6 mm from the apex (B plane), the oval shape was the most common, and the dumbbell shape was also seen in the horizontal plane perpendicular to the tooth axis at a distance of 3 mm from the apex (C plane). These results suggest that, although the root canal morphology of the mandibular central incisors is usually simple, the possibility that some main root canals may be difficult to clean and that an accessory root canal may be present should be borne in mind when carrying out pulp chamber enlargement and root canal treatment.